Mining hangs on Generating DAG in progress

Question

I am trying to initialize rpc using the below command and start miner using miner.start(1);

geth --rpcapi eth,web3,personal --rpc --networkid=15

Mining starts successfully with below logs but it doesn't proceed further and hangs here only.

INFO [08-28|18:20:52.808] Generating DAG in progress               epoch=1 percentage=98 elapsed=12.725s
INFO [08-28|18:20:53.063] Generating DAG in progress               epoch=1 percentage=99 elapsed=12.981s
INFO [08-28|18:20:53.065] Generated ethash verification cache      epoch=1 elapsed=12.983s

Things i tried till now.

1. https://ethereum.stackexchange.com/a/13610/41204

   action : 64GB RAM 128GB HD and 16CPU so this is not the problem i guess.

2. https://stackoverflow.com/a/46430217/6572971

   action : Have set primary account using eth.defaultAccount=eth.coinbase which returns "0x-----"

3. https://ethereum.stackexchange.com/a/39000/41204

   action : Have done as suggested but no luck.